Level Book & Closure Calculator
Calculate reduced levels from BS, IS and FS observations, verify the arithmetic closure and produce adjusted levels with a professional field report.
Level book information
| # | Point / station | BS (m) | IS (m) | FS (m) | Distance (m) | Remarks |
|---|
Change points: enter both the FS from the old setup and the BS from the new setup on the same row. Distance should be the horizontal segment distance from the previous point.
Results and closure check
| # | Point | BS | IS | FS | HOC | Rise | Fall | RL | Correction | Adjusted RL | Remarks |
|---|
Level book calculation workflow
Enter the known levels
Enter the reduced level of the starting benchmark and the independently known RL of the closing benchmark or closing point.
Add field observations
Record each backsight, intermediate sight and foresight in sequence. For a change point, place the FS and the next BS in the same row.
Enter distances
Add the horizontal distance from the previous point if the closure correction must be distributed proportionally to distance.
Check and export
Calculate the book, review the arithmetic and tolerance status, then export the editable CSV or print the signed project report to PDF.
Height of Collimation calculation
The height of collimation is calculated as the known reduced level plus the backsight. Each intermediate or foresight level is then the current HOC minus the staff reading. When a row contains both FS and BS, the point is treated as a change point and a new HOC is established.
Rise and Fall cross-check
The calculator also compares consecutive effective staff readings. A smaller next reading represents a rise and a larger reading represents a fall. At change points the foresight closes the old setup and the backsight starts the new setup.
Closure and misclosure
The computed closing RL is compared with the known closing RL. Their signed difference is the misclosure. The report displays both the raw result and the correction applied to each point.
Arithmetic check
A valid level book should satisfy ΣBS − ΣFS = last calculated RL − starting RL. A non-zero arithmetic difference normally indicates incomplete, duplicated or incorrectly classified observations.
Level book calculator FAQ
What are BS, IS and FS in levelling?
BS is a backsight taken to a point of known or carried RL, IS is an intermediate sight, and FS is the final reading before moving the instrument or closing the run.
How should I enter a change point?
Use one row for the change point and enter both the foresight from the old setup and the backsight from the new setup. The calculator obtains the CP RL from the FS and then establishes the new HOC from the BS.
How is the allowable closure calculated?
The default comparison is ±C√K millimetres, where C is the editable tolerance coefficient and K is the total run distance in kilometres. Your contract may specify a different rule.
Does the tool replace a surveyor's check?
No. It assists calculation and reporting. Raw observations, benchmark provenance, instrument checks, collimation tests and project-specific tolerances remain the responsibility of the competent surveyor.